1. Field of the Invention
The invention pertains to a hydrodynamic torque converter of the type having a pump wheel and a turbine wheel, wherein each wheel has an outer shell, an inner shell, and a plurality of vanes connecting the shells.
2. Description of the Related Art
A hydrodynamic torque converter with a hydrodynamic circuit including at least one pump wheel and one turbine wheel is known from EP 0 070 662 A1, where both the pump wheel and the turbine wheel are provided with an outer shell which accepts a set of vanes serving to form flow chambers, and where, on the edges facing away from the associated outer shell, the vanes are provided with an inner shell, which acts as part of an internal torus. The vanes of the turbine wheel have connecting elements in the form of integral tabs both on the edges facing the outer shell and on the edges facing the inner shell; so that the tabs can connect the vanes to the shells, they pass through openings in the latter and have a predetermined minimum overhang with respect to the edge of the associated vane. This minimum overhang makes it possible for the connecting elements to be plastically deformed. The tabs thus grip the rear surface of the shell, i.e., the surface facing away from the vanes, and thus fasten the vanes to the shells. In the case of the pump wheel, the vanes are connected in the same way to the inner shell, but a different approach is preferred for connecting the edges of the vanes facing the outer shell to the outer shell, because it is necessary not only for vanes to be attached permanently to the pump wheel but also for the converter housing to be absolutely leak-tight. For this reason, the outer shell of the pump wheel is not interrupted by openings for the connecting elements but is provided instead only with recesses for them.
As can be seen from the single figure in EP 0 070 662 A1, two connecting elements are provided to connect the vanes of the pump wheel and of the turbine wheel to their inner shells, whereas three connecting elements are provided to attach the vanes of the turbine wheel to its outer shell. Deciding on this number of connecting elements for the outer shell and the inner shell, preferably for the connections in the turbine wheel, may be reasonable in the case of hydrodynamic torque converters with hydrodynamic circuits of the conventional design, but this European Offenlegungsschrift discusses a special converter design, in which the hydrodynamic circuit, designated H in the figure, is a comparatively long distance Ri away from a center axis A, for which reason these types of torque converters are said in professional circles to have the “high/round” design. High/round designs offer the advantage that the hydrodynamic circuit, because of its considerable distance from the central axis in the radial direction, has only a limited height H, so that, when both the pump wheel and the turbine wheel are designed with a cross section approximating the ideal circular form, it is necessary for the hydrodynamic circuit to extend only a limited distance in the axial direction, as a result of which excellent hydrodynamic properties can be achieved in only a small amount of axial space. Because of the very sharp curves of the shells, however, it is difficult to thread the vanes and their connecting elements into the proper positions required for the attachment of the vanes to the shells, and the openings in the shells required to accept the connecting elements must be designed with the smallest possible oversize with respect to the connecting elements to ensure the required strength of the connection.